1. Field of the Invention
The present invention relates to an exposure control of an image-taking apparatus, and more particularly, to an apparatus image-taking apparatus which has a distance detection unit for detecting distances of a plurality of points and an illumination unit.
2. Description of the Related Art
In image-taking apparatuses such as silver-halide film cameras, digital cameras, etc., in which operations such as an exposure setting, a focusing adjustment, etc. are automated, users who are not familiar with camera operations are able to take proper images by using image-taking apparatuses when objects satisfy normal conditions.
When an object is dark, by flashing an illumination unit built in a camera or connected to a camera, it is possible to operate the camera so as to improve the luminance of the object. On the other hand, when an object is dark and also when the object is far away from the illumination unit so that illuminated light is faint at the object, it is possible to increase the luminance of the object for a camera by using a longer exposure time.
However, when an exposure time becomes longer, there is a possibility to be influenced from camera shake. For this reason, during image-taking which requires a longer exposure time than a certain exposure time (for example, one-sixths of a second), it may happen that a camera has an insufficient exposure time, and it is arranged to perform image-taking by setting an upper limit to the exposure time (maximum exposure time) by preferentially repressing camera shake. In this case, the setting time is referred to, hereinafter, as a “shutter finish time” and set to, for example, one-sixth of a second. Further, the exposure time defined here includes both the exposing time determined by a mechanical shutter which shields light from reaching an image-pickup element by a light damper blade and the exposing time determined by an electronic shutter made of a photoelectric conversion element such as CCD. By forcing image-taking into finishing within the exposure time of one-sixth of a second, it is possible to repress camera shake, but there may be cases where an exposure can be insufficient for objects.
For this reason, Japanese Patent Application Laid-Open No. 2002-229092 discloses a structure in which camera shake and low exposure are arranged to be balanced by changing a shutter finish time according to image-taking modes.
However, in the structure which selects the shutter finish time according to an image-taking mode, when a user does not have sufficient knowledge of a camera, it is possible for the user to select an improper shutter finish time. For example, when the distance of a background object is similar to the distance from a main object, the luminance of the background becomes bright due to light irradiated from an illumination unit, and it is not necessary to make the shutter finish time longer. In such cases, since the possibility of insufficient exposure is low, it is more important to repress camera shake, and the shutter finish time should be shortened. On the contrary, when the distance from the background object is significantly larger compared to the distance from the main object, it is necessary to make the shutter finish time longer in order to perform image-taking by obtaining a brighter background.
As described above, even when the luminance of a object is substantially similar, it is preferable to select the shutter finish time appropriate to the distance from the camera to the background object.